This is from another thread, some useful info:
This is a paragraph pasted from the Sol20.org site:
If you want to try and download these programs to your Sol, here's how to do it.
Grab the *.ent file you are interested from one of the tables below.
Connect a serial cable from your PC to your Sol
Set the baud rate, data bits, parity bits, and stop bits the same on the two machines. I have difficulty getting my Sol to transfer reliably if the baud rate is higher than 1200. YMMV.
Test that the link works. Use the TERM command to do so.
On the Sol, type "SET I=1". This makes it accept subsequent input from the serial port, as if you were entering it from the keyboard.
On the PC, transfer the *.ent file over the serial link as a straight ASCII file.
To run the program, type "EX xxxx", where xxxx is the load address, and off she goes!
Mike Douglas has having troubles getting ENT programs to load into his machine at 9600 baud. After puzzling over it a bit, he found that some .ENT files are saved with CR/LF line endings. He found that deleting the line feeds from the files and telling his term program (TerraTerm) to insert a 100 ms delay after each CR fixed it -- he could then reliably send data at 9600 baud. That 100ms is to give SOLOS enough time to scroll the screen after each line.
You just do it on the Sol , with Solos running in the usual way, after you have done a reset, or after the Sol is powered when it comes up with the usual cursor. The TERM command that you type on the Sol is just a good way to test the serial link and that it is working in both directions properly. As noted the SET I=1 command you type on the SOL, makes the SOL ready to receive a file to memory, typically a .ENT file that specifies the starting address and memory addresses that the file will get loaded to in the SOL's RAM. Sending a file to the SOL this way, with TeraTerm at least, the option to select is just "SEND" not the "transfer" options which include Xmodem. They are used when you want to transfer other file formats like .COM files etc.
When the .ENT file is sending, you will see the addresses and bytes appearing on the SOL's VDU, just as if somebody was typing them in at a high speed. So its easy to see that you got the whole file and it went to the correct addresses.
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I'm sure I drew a diagram up of the cable arrangements I use and put it on a thread, but I can't seem to see it anywhere, I'll look for it.
If you are using a USB, you would need a USB serial converter which has a small chip in it. There was some episode, a while back, involving many fake chips and some manufacturer somehow deactivated their product line in some vindictive event, but I cannot recall the details.I have avoided trying to use a USB interface as it threw in more variables.